In our U.S. Pat. No. 6,797,166 issued Sep. 28, 2004, the contents of which are incorporated herein by reference, there is described and claimed a filter underdrain apparatus and a method of utilising such an apparatus during water filtration. The technique utilises certain improvements in underdrains which have worked well in water filtration. The present invention extends such improvements in water clarification and relates to improvements which take place upstream of the water filtration.
In water clarification, tube settlers which comprise a plurality of extended length tubes generally molded into a composite tube settler apparatus which is inserted into a water clarification cell. The water to be clarified runs through the tubes of the tube settler apparatus and deposits sediments and other solids in the tubes. The purpose of the tube settler apparatus is to increase the surface area exposed to the water such that the effective settling area is increased.
A problem with such tube settlers is that because of the solid deposition within the tubes, the tubes may become plugged. If the tubes become plugged, the performance and efficiency of the settlement process is adversely effected. In certain clarification procedures, the tube bundles can become so fouled with heavy sludge, collapse of the tube bundles and even the underlying support structure for the tube bundlers can occur. This is a costly and time consuming problem. Thus, intermittent cleaning of the tubes to remove the buildup of sludge over time is required.
One existing method of cleaning the tubes is by manually washing the tube bundles from above with a high pressure water stream directed at the tube bundles. While the tube bundles which are exposed to the water stream are cleaned in a satisfactory manner using this technique, the tube bundles that are not so exposed such as those beneath the collection troughs and walkways are not cleaned thereby detracting from the overall performance of the tube settler apparatus.
Another technique is colloquially called “air lancing” which instead of water, uses high pressure air which plays on the tube openings in the settler. The tube bundles are, however, sensitive to the high pressure air and damage to the tube settler assembly can occur. Similar to the manual washing technique, not all tube bundles can be reached with the high pressure air. Also likewise, the procedure is labor intensive.
A further technique used provides a fixed air distribution grid under the tube settler assembly. While this technique shows promise, existing air distribution grids do not reach a substantial portion of the tube bundle area and no air distribution into the tubes immediately above the support structure for the tube settler assembly is provided. Existing air grids, therefore, do not clean the tube settler assembly in these locations which is disadvantageous.